Field of Invention
The present invention relates to methods and apparatus for raising or lowering a volume of a fluid such as water using an Archimedes screw-type device. More specifically, the present invention incorporates a strake shape as a blade to increase the volume of fluid previously obtained using a helicoid shape.
Description of Related Art
The Archimedes Screw is a device used to raise or lower a fluid, usually water, from one level to another. When used for raising water, energy is supplied to turn the screw, and when used to lower water, energy is generated by the turning of the screw.
The Archimedes Screw is one of the oldest machines in use. Its invention has traditionally been credited to Archimedes, an ancient Greek mathematician and engineer, who lived in the third century BC.
FIG. 1 shows the basic design of an Archimedes Screw from antiquity that is used to raise water. It consists of an inner cylinder or core wrapped by blades (also called “starts” or “flights”) and an outer cylinder enclosing the blades. Its bottom end is immersed in a body of water (the “lower reservoir”) and water is raised to the top end (the “upper reservoir”). When tilted as shown, water is trapped in “buckets” formed by the two cylinders and the blades. As the entire devise is rotated by the crank at the top, the action of the screw motion causes these buckets of water to be lifted from the lower to the upper reservoir.
In antiquity and up to the last century, the main uses of the Archimedes Screw were to irrigate fields from a low-lying stream or river; to raise storm water out of low-lying land; and to drain water from mines.
FIG. 2 is an illustration of an Archimedes Screw described by the Roman Engineer Vitruvius in the first century BC. The inner cylinder is shaped from the trunk of a tree, the outer cylinder is constructed from planks, and the eight intertwined blades are built up from the long flexible twigs from willow trees. All parts were nailed together and sealed with tar to eliminate leakages. The blade shape in FIG. 2 is called a helicoid and has so far been the only shape used for Archimedes Screws.
Present-day uses of the Archimedes Screw include applications in wastewater treatment facilities, low-lying land-pumping stations (such as found in The Netherlands or the Gulf coast region), irrigation systems, rain-detention dams, flood-detention dams, fish-conveyor systems, or water sports and recreational activities, all using the helicoid blade design.
Within the United States the Archimedes Screw is used most frequently in wastewater treatment plants. FIG. 3 shows seven Archimedes Screws used to pump wastewater in a treatment plant in Memphis, Tenn., USA. Each of these Screws is 96 inches (2.44 meters) in diameter and can lift 19,900 gallons per minute. The Screws were manufactured by the Lakeside Equipment Company of Bartlett, Ill., USA. In modern installations, the outer cylinder that covered the screw in antiquity is usually replaced by a stationary half-cylinder trough in which the screw blades attached to the inner cylinder rotate. When used to raise water, the screw is turned by an electric or diesel motor.
Within the last twenty years, a new application of the screw has been discovered in the generation of electricity. For such applications, Archimedes Screws are also called hydropower screws. FIG. 4 shows one such installation in Germany in which two screws are set next to a stream and part of the flow of the stream is diverted to the top of the screws. The weight of the water causes the screws to turn, driving an electrical generator located in the shed. There are hundreds of sites throughout Europe equipped with these hydropower screws, and they are now becoming available in the United States.
FIG. 5 shows screws in a manufacturing plant. Almost all screws manufactured today have 3, 4, or 5 intertwined blades, as shown.
In each of the uses described above, the screw is designed with a helicoid shape that requires extensive, high-cost, manufacturing procedures in fabricating the helicoid blade. The high cost is primarily due to the stretching and compressing necessary to obtain the desired shape. The helicoid shape itself has a limited fluid volume available for filling each bucket during movement of the screw.
Therefore, there exists a need to increase the capacity of individual buckets and thus improve the efficiency of fluid being moved through the screw and also improve the manufacturing process to reduce the high cost of fabricating a helicoid shape.